So, I picked up a few super capacitors from mouser, rated for 10F @ 2.7V. My question: Is there a formula for determining how long it takes for a cap to reach full capacity? Is it the inverse of its discharge rate?

I've been playing around with 1.5v coin battery and the super cap, and after only about 15 seconds of contact with the battery terminals, the cap has enough juice to run a small pager motor for 2-3 minutes! I figure a small array of photodiodes like the bpw34 (http://www.sparkfun.com/commerce/product_info.php?products_id=9541) could be used to power a small circuit setup for occasional bursts of activity, possibly even a full MCU like the ATTiny at the 1.8v mode.

A single 'Farad' is huge, let alone 10.... I would be very careful handling capacitors as large as what you are talking about-- the voltage is low, but the current is NOT.

Super caps are useful in data retention circuits like RAM in computers and such, where they have a battery to keep them viable. They allow for replacement without losing the data. They can also be useful in low power circuits where an occasional surge is needed for whatever, without putting a load on the battery which could affect the supply voltage.

The largest ones I have encountered were 2F at 5 V. Can't imagine a 10F cap. It would be interesting to play with though.

i am looking for a supercap to use with my alarm clock and came across this on ebay 2.7v 200farad insaneness. ebay link